is it good English: you know pretty well , you know perfectly well ?

Question

Answer

Hey do you know Delfina?  "Yeah I know her pretty well".

What time are we going Jennifer?  "You know perfectly well, I've told you a million times. 6pm!"

Good English, different meanings

Answer

Yes, they both are correct. But when you say i know it pretty well, you are saying that you have quite a good idea about something, little chance then to be wrong.        On the other side, when you say that you know perfectly well, then there is no chance to be wrong!